It has long been recognized that hydrogen is an extremely energetic element and an excellent fuel to fuel electro-chemical, electric power generating fuel cells.
The prior art has long sought to provide a simple, highly effective and efficient hydrogen-fueled fuel cell structure that is such that is has practical utility and such that it lends itself to commercial exploitation and economical usage. The prior art has failed to provide such a fuel cell as is evidenced by the unavailability and/or the absence of any such cell in industry and in the marketplace.
The reasons for the failure of the prior art to provide a hydrogen-fueled fuel cell of practical utility are manifold and are sufficiently well-known to those skilled in the art so that all reasons need not be enumerated. One notable reason such a fuel cell has not been provided by the prior art resides in the fact that the use of gaseous fuels in fuel cells, as a general rule, presents a multitude of structural problems which, prior to my invention, have prevented the establishment of such a cell which is sufficiently small, compact and/or sufficiently strong and durable for common everyday usage. Another notable reason such a fuel cell has not been provided by the prior art resides in the fact that substantially pure hydrogen gas must be used (for numerous reasons) and the fact that pure hydrogen gas is costly and complicated to produce, store, handle and dispense.
It has long been common practice to easily and economically produce impure hydrogen-enriched gas by what is commonly called Steam-Methane Reforming or Steam-Methanol Reforming methods and processes wherein hot vaporous or gaseous mixtures of steam (water) and either methane or methanol are moved into contact with a heated reformer catalyst, such as a porous nickel body in which they react and are reduced to a mixture of hydrogen and carbon dioxide gases. While the gaseous mixtures thus produced find many uses, they are, due to the carbon dioxide and other impurities, unsuitable for use in fuel cells.
To separate the hydrogen from the above noted hydrogen-enriched gaseous mixtures, it must be and often is subjected to other and separate processes.
It has long been recognized that most metals, in imperforate, non-porous form, can be permeated by hydrogen and that when hydrogen permeates them, the gas diffuses, or is reduced to hydrogen ions and free electrons. The hydrogen ions and free electrons, moving from said hydrogen-permeable metals, recombine to establish pure hydrogen gas. Thus, such hydrogen-permeable metals are, in effect, and are commonly used as "Separator Filters" to separate hydrogen gas from hydrogen-enriched feed gas mixtures, to produce pure hydrogen.
The hydrogen permeability of different metals varies widely. Accordingly, when seeking to separate and purify hydrogen from hydrogen-enriched feed gas mixtures, it is prudent to select a hydrogen-permeable metal or metal alloy which is highly permeable and which otherwise has those physical characteristics which will enable its practical use.
The permeability of hydrogen through a hydrogen-permeable metal membrane, layer, lamina or strata, as hydrogen ions is dependent upon several factors. The most important factors are the thickness of the metal membrane or strata, the pressure differential between the upstream or supply-side of the strata, which must be the high pressure side, and the downstream or discharge side of the strata which is the low pressure side, and the temperature of the metal strata. As a general rule, the rate of permeability is inversely proportional to the thickness of the metal strata. Thus, for greatest effectiveness and for certain other reasons, such as size, cost, and weight, such a metal strata should be made as thin as is possible and/or practical. Elevating the temperature of such hydrogen-permeable metal strata, as a general rule, expands the metals and opens the crystalline lattice structure thereof to appreciably enhance the permeability thereof. The temperatures to which different hydrogen-permeable metals can be safely elevated and the effects heating of such metals has on their permeability varies and is a factor to consider when selecting such a metal for such use. The pressure differential between the high pressure upstream side and the low pressure or downstream side of hydrogen-permeable strata used to separate and purify hydrogen from gas mixtures is believed self-evident, that is, it clearly and obviously induces and accelerates the rate of permeation of hydrogen through the strata.
I have found that a membrane or strata of hydrogen-permeable palladium or palladium-silver alloy, which has a high rate of hydrogen-permeability, can be effectively made as thin as 0.0005 inches, heated to temperatures in excess of 800.degree. F. and, if suitably supported, can be effectively and safely subjected to pressure differentials in excess of 700 p.s.i. Such a hydrogen-permeable metal strata is particularly satisfactory for use in practicing my invention, as will hereinafter be described.
For a more comprehensive explanation and better understanding of hydrogen-permeable metal membranes or strata and their use in separating and purifying hydrogen from hydrogen-enriched mixtures of feed gas, reference is made to U.S. Pat. No. 2,824,620 issued to A. J. De Rosset on Feb. 25, 1958 and entitled Purification of Hydrogen Utilizing Hydrogen-Permeable Membranes.